Mycobacterium leprae, also known as Hansen's bacillus, is the primary causative agent of leprosy. This bacteria affects the skin, peripheral nerves, and mucosa of the upper respiratory tract. There are several synonyms for Mycobacterium leprae, including Hansen's disease bacillus, lepra bacillus, and Hansen's coccus. Some people also refer to it as the leprosy bacteria or simply leprosy germ. Regardless of the name used, this bacteria can cause significant damage to the body, leaving lasting physical effects if not treated early. Early diagnosis and treatment of Hansen's bacillus are essential to prevent further complications and limit damage to affected tissues.